The present invention relates to a motion detection apparatus and particularly to such apparatus having a sensitivity control to control the response to motion.
In many industrial controls and applications the presence and amplitude of selected motion as well as direction is detected and displayed or otherwise employed in a control to maintain a predetermined characteristic. Although such systems have been suggested, they have generally been designed with a separate sensor or pick-up connected at a remote location to the processing circuitry. Motion detectors are commonly employed in connection with industrial machines such as metal working presses, cutting tools, conveying apparatus and the like, where the rotational speed of a shaft of a machine is monitored to indicate abnormal operating conditions. For example, in the case of a metal working press, if the machine should become jammed, preventing press operation, some safety device should be incorporated to rapidly terminate machine operation to prevent damage to the apparatus or to the personnel operating the apparatus. A motion detector coupled to the drive shaft which can accurately determine shaft rotation and function as a zero or low speed detector may provide a suitable signal for operation of a simple safety interlock. In other systems, it may be desirable to limit the speed to a maximum rotational speed and provide an indication of an overspeed condition and/or operate a safety interlock or speed reducing control means. Rotary motion sensing is thus highly desirable to produce an interrelated indication and/or control means. In order to adapt a motion speed detector to the various applications and conditions encountered, however, requires that the apparatus includes means to effectively adjust the control to the particular limitations. In many applications, a mechanical motion may be conveniently transformed into an electrical output which is subsequently processed. The transformation is effected by a suitable transducer and may conveniently be a digital encoder which develops a train of electrical pulses in accordance with the amplitude or amount of motion of an element. Various encoders such as mechanical, magnetic and photoelectric types have been employed. Photoelectric encoders provide a highly satisfactory means from a practical standpoint. They have generally employed special infrared light system or conventional incandescent lamps which are not particularly adapted to a compact unit which can be machine mounted.
Generally in the prior art system, motion detector apparatus has normally employed a local pick-up unit connected to a remotely located signal processing unit by low voltage wiring. Such a system is subject to inducement of noise signals and the like on the low voltage wiring with the resulting possible false reading.
Although certain machine mounted systems have been suggested, electronically processed signal systems have generally not been satisfactorily employed because of the effects of vibration. Thus, as the motion approaches or reaches a stop or very slow state, slight vibration of the machine and/or shaft system can result in false driving of the output circuit or system. For example, U.S. Pat. No. 2,685,082 to Beaman et al discloses an incandescent lamp and optical pick-up system with a pair of offset sensors. If the unit is vibrated with the lamps immediately adjacent to a signal generating area of the disc 21, false digital output signals can be generated as a result of such vibrational movement and drive the counter. A more recent U.S. Pat. No. 3,449,588 discloses a photoelectric encoder employing a pair of relatively rotating graded disc members for producing four interrelated signals driving a logic circuit to determine the magnitude and direction of relative movement. The system employs a count channel and a separate direction channel to selectively enable the count channel having a pair of outputs selectively enabled by the separate directional control channel.
The electronic systems have not been developed, however, as an integrated machine mounted unit which can be readily adjusted to various responses and environmental and machine environments.